Imaging lens

ABSTRACT

An imaging lens includes plastic-made first, second, third, and fourth lens elements arranged in the given order from an object side to an imaging side. The first lens element has a positive focusing power and is biconvex. The second lens element has a negative focusing power, is biconcave, and has an abbe number not greater than 30. The third lens element has a positive focusing power and has a convex imaging-side surface facing toward the imaging side. The fourth lens element has an imaging-side surface formed with a concave area in a vicinity of an optical axis of the fourth lens element. The imaging lens further includes an aperture stop disposed between the first and second lens elements.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/013,164, filed Jan. 25, 2011, which claims priority to TaiwaneseApplication No. 099130640, filed on Sep. 10, 2010, the disclosures ofwhich are hereby incorporated by reference in their entirety for allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens and an electronicapparatus having the same, more particularly to an imaging lens withfour lens elements and to an electronic apparatus having the same.

2. Description of the Related Art

In recent years, various electronic devices are designed to includeimaging lenses and image sensors for image-capturing and video-recordingcapabilities. To improve portability and imaging performances whilereducing dimensions and weights of the electronic devices, differentcombinations of lenses are installed in the electronic devices.

U.S. Pat. No. 7,453,654 discloses an imaging lens with four lenselements of different optical characteristics, one of which is aspherical glass lens element while remaining three of which are plasticaspherical lens elements for enhancing image quality. However, thespherical glass lens element is difficult to fabricate due to its smalldimensions and radius of curvature, and therefore has drawbacks such ashigh costs and weight.

Besides, although the spherical glass lens element is able to achieve arelatively high positive refracting power at a relatively small radiusof curvature such that an overall length of the imaging lens may besignificantly reduced, the spherical glass lens element is known toexhibit high chromatic aberration due to its low Abbe number.

U.S. Pat. No. 6,476,982 discloses an imaging lens with first and secondlens elements thereof adhesively bonded to each other to thereby reducechromatic aberration. Nevertheless, such an approach to reduce chromaticaberration requires a strong bonding between the first and second lenselements, which is often difficult to achieve especially if the firstand second lens elements are made of different materials, e.g., glassand plastic, respectively. While the first and second lens elements mayboth be made of glass, costs and weight of the imaging lens will, as aresult, be compromised.

U.S. Pat. No. 7,466,497 discloses an imaging lens with four plastic lenselements. Although the imaging lens has a relatively short overall focallength and maybe fabricated at a relatively low cost, the imaging lensis known to exhibit high chromatic aberration.

Therefore, the need for a low cost, low weight imaging lens thatexhibits low chromatic aberration still exists in the market.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an imaginglens capable of alleviating the drawbacks of the aforesaid imaginglenses of the prior art.

Accordingly, an imaging lens of the present invention includes first,second, third, and fourth lens elements arranged in the given order froman object side to an imaging side.

The first lens element is made of plastic, has a positive focusingpower, and is biconvex. The second lens element is made of plastic, hasa negative focusing power, is biconcave, and has an abbe number notgreater than 30. The third lens element is made of plastic, has apositive focusing power, and has a convex imaging-side surface facingtoward the imaging side. The fourth lens element is made of plastic, andhas an imaging-side surface facing toward the imaging side and formedwith a concave area in a vicinity of an optical axis of the fourth lenselement. The imaging lens further includes an aperture stop disposedbetween the first and second lens elements.

Another object of the present invention is to provide an electronicapparatus having an imaging module.

Accordingly, an electronic apparatus of the present invention includes ahousing and an imaging module that is disposed in the housing. Theimaging module includes an imaging lens having an object side and animaging side, and an image sensor disposed at the imaging side.

The imaging lens includes first, second, third, and fourth lens elementsarranged in the given order from the object side to the imaging side.The first lens element is made of plastic, has a positive focusingpower, and is biconvex. The second lens element is made of plastic, hasa negative focusing power, is biconcave, and has an abbe number notgreater than 30. The third lens element is made of plastic, has apositive focusing power, and has a convex imaging-side surface facingtoward the imaging side. The fourth lens element is made of plastic, andhas an imaging-side surface facing toward the imaging side and formedwith a concave area in a vicinity of an optical axis of the fourth lenselement. The imaging lens further includes an aperture stop disposedbetween the first and second lens elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments with reference to the accompanying drawings, of which:

FIG. 1 is a schematic diagram illustrating the first preferredembodiment of an imaging lens according to the present invention;

FIG. 2 illustrates plots of sagittal astigmatism, tangentialastigmatism, and distortion aberrations of the imaging lens of the firstpreferred embodiment;

FIG. 3 illustrates ray fan plots of the imaging lens of the firstpreferred embodiment at different angles of view;

FIG. 4 is a schematic diagram illustrating the second preferredembodiment of an imaging lens according to the present invention;

FIG. 5 illustrates plots of sagittal astigmatism, tangentialastigmatism, and distortion aberrations of the imaging lens of thesecond preferred embodiment;

FIG. 6 illustrates ray fan plots of the imaging lens of the secondpreferred embodiment at different angles of view;

FIG. 7 is a schematic diagram illustrating the third preferredembodiment of an imaging lens according to the present invention;

FIG. 8 illustrates plots of sagittal astigmatism, tangentialastigmatism, and distortion aberrations of the imaging lens of the thirdpreferred embodiment;

FIG. 9 illustrates ray fan plots of the imaging lens of the thirdpreferred embodiment at different angles of view;

FIG. 10 is a schematic diagram illustrating the fourth preferredembodiment of an imaging lens according to the present invention;

FIG. 11 illustrates plots of sagittal astigmatism, tangentialastigmatism, and distortion aberrations of the imaging lens of thefourth preferred embodiment;

FIG. 12 illustrates ray fan plots of the imaging lens of the fourthpreferred embodiment at different angles of view; and

FIG. 13 is a schematic partly sectional view illustrating the preferredembodiment of an electronic apparatus, which includes a housing and animaging module, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present invention is described in greater detail, it shouldbe noted that like elements are denoted by the same reference numeralsthroughout the disclosure.

Referring to FIG. 1, the first preferred embodiment of an imaging lens 2of the present invention includes a first lens element 3, an aperturestop 7, a second lens element 4, a third lens element 5, a fourth lenselement 6, and an optical filter 8 arranged in the given order from anobject side to an imaging side. Each of the first, second, third, andfourth lens elements 3, 4, 5, 6 is made of plastic, and has anobject-side surface 31, 41, 51, 61 and an imaging-side surface 32, 42,52, 62. The first and second lens elements 3, 4 have a gap with a widthpreferably not narrower than 0.08 mm formed therebetween. When lightenters the imaging lens 2, it travels through the first lens element 3,the aperture stop 7, the second lens element 4, the third lens element5, the fourth lens element 6, and the optical filter 8 in the givenorder, and eventually forms an image at an imaging plane 10 disposed atthe imaging side.

The first lens element 3 is a biconvex lens element with a positivefocusing power (i.e., a positive diopter or a positive refractingpower). The second lens element 4 is a biconcave lens element with anegative focusing power, and has an abbe number not greater than 30. Thethird lens element 5 has a positive focusing power, and the object-sidesurface 51 and the imaging-side surface 52 thereof are a concave surfaceand a convex surface, respectively. The fourth lens element 6 has anegative focusing power, the object-side surface 61 thereof is awavelike surface having a convex area 611 in a vicinity of an opticalaxis (I) of the fourth lens element 6, and the imaging-side surface 62thereof is a wavelike surface having a concave area 621 in the vicinityof the optical axis (I) of the fourth lens element 6. The aperture stop7 is disposed between the first and second lens elements 3, 4, and isdisposed on the imaging-side surface 32 of the first lens element 3 inthis embodiment. The optical filter 8 is a flat glass panel, and has anobject-side surface 81 facing toward the object side, and animaging-side surface 82 facing toward the imaging side and parallel tothe object-side surface 81.

Table 1 shows optical parameters of the lens elements 3-6, the opticalfilter 8, and the imaging plane 10.

TABLE 1 Radius of Curvature Thickness Refractive Abbe Surface (mm) (mm)Index Number First 31 1.142 0.300 1.544 56.12 Lens 32 −3.234 0.086element 3 Second 41 −6.872 0.200 1.607 27.00 lens 42 1.988 0.200 element4 Third 51 −1.340 0.315 1.531 56.00 Lens 52 −0.633 0.080 element 5Fourth 61 0.933 0.300 1.531 56.00 Lens 62 0.671 0.313 element 6 Optical81 ∞ 0.210 1.517 64.00 filter 8 82 ∞ 0.288 Imaging — ∞ −0.004 — — plane10

The object-side surfaces 31, 41, 51, 61 and the imaging-side surfaces32, 42, 52, 62 are aspherical surfaces, and may be defined by thefollowing equation (1):

$\begin{matrix}{{Z(X)} = {\frac{x^{2}/r}{1 + \sqrt{1 - {\left( {1 + K} \right)\frac{x^{2}}{r^{2}}}}} + {AX}^{4} + {BX}^{6} + {CX}^{8} + {DX}^{10} + {EX}^{12} + {FX}^{14}}} & (1)\end{matrix}$

wherein (Z) represents an axis extending along the optical axis (I), (X)represents an axis extending perpendicular to the optical axis (I), and(r) is the radius of curvature (see Table 1). Moreover, Tables 2, 3 and4 show conic constants (K), and higher-order aspherical surfacecoefficients (A), (B), (C), (D), (E), (F) of the object-side surfaces31, 41, 51, 61 and the imaging-side surfaces 32, 42, 52, 62.

TABLE 2 Surface K A B 31 −1.8593E+00 0.0000E+00 2.2558E−02 32 2.5855E+010.0000E+00 1.1308E+00 41 8.8402E+01 0.0000E+00 1.3501E+00 42 6.7216E+000.0000E+00 1.6877E−01 51 2.5264E+00 0.0000E+00 −2.6674E−01 52−5.0546E−01 0.0000E+00 −1.5400E−01 61 0.0000E+00 −1.0100E+00 5.4318E−0162 −1.3578E+00 −9.6118E−01 8.5293E−01

TABLE 3 Surface C D E 31 −1.1958E+00 0.0000E+00 0.0000E+00 32−7.3494E−01 0.0000E+00 0.0000E+00 41 0.0000E+00 0.0000E+00 0.0000E+00 420.0000E+00 0.0000E+00 0.0000E+00 51 0.0000E+00 0.0000E+00 0.0000E+00 520.0000E+00 0.0000E+00 0.0000E+00 61 −1.2084E+00 2.6891E+00 −2.1573E+0062 −5.9839E−01 4.0733E−01 −3.0081E−01

TABLE 4 Surface E 31 0.0000E+00 32 0.0000E+00 41 0.0000E+00 420.0000E+00 51 0.0000E+00 52 0.0000E+00 61 0.0000E+00 62 0.069492928

Shown in FIG. 2 from left to right are plots of sagittal astigmatism(along a sagittal plane with respect to the imaging plane 10),tangential astigmatism (along a tangential plane with respect to theimaging plane 10), and distortion aberrations of the imaging lens 2 ofthe first preferred embodiment at three representative wavelengths (626nm, 588 nm, and 486 nm). As shown in the plots of sagittal andtangential astigmatisms, the imaging lens 2 has a range of focaldistances not exceeding ±0.05 mm within the whole angle of view at eachof the representative wavelengths. Furthermore, in each of the plots ofsagittal and tangential astigmatisms, curves that respectively representthe three representative wavelengths are relatively similar, whichindicates that the imaging lens 2 of the first preferred embodimentexhibits relatively low chromatic aberration. Moreover, the distortionaberrations that occur in the imaging lens 2 of the first preferredembodiment have a range within ±0.3%. Therefore, the imaging lens 2 ofthe first preferred embodiment of the present invention has significantimprovement over the prior art in terms of optical performance. FIG. 3illustrates ray fan plots of the imaging lens 2 of the first preferredembodiment at normalized half-angles of view of 1, 0.8, and 0, whichcorrespond to relative angles of view of 37.41°, 31.33°, and 0°,respectively. It is apparent that the imaging lens 2 is able to achievelow optical aberrations, and an angle of view of 74.82.degree., which iswider than those generally achievable by conventional imaging lenses ofthe prior art.

Referring to FIG. 4, the second preferred embodiment of this inventionhas a configuration almost identical to that of the first preferredembodiment. The first lens element 3 is a biconvex lens element. Thesecond lens element 4 is a biconcave lens element. The object-sidesurface 51 and the imaging-side surface 52 of the third lens element 5are a concave surface and a convex surface, respectively. Theobject-side surface 61 of the fourth lens element 6 is a wavelikesurface having a convex area 611 in the vicinity of the optical axis (I)of the fourth lens element 6, and the imaging-side surface 62 of thesame is a wavelike surface having a concave area 621 in the vicinity ofthe optical axis (I) of the fourth lens element 6. The aperture stop 7is disposed between the first and second lens elements 3, 4, and isdisposed on the imaging-side surface 32 of the first lens element 3 inthis invention.

Table 5 shows optical parameters of the lens elements 3-6, the opticalfilter 8, and the imaging plane 10 in the second preferred embodiment.

TABLE 5 Radius of Curvature Thickness Refractive Abbe Surface (mm) (mm)Index Number First 31 1.039 0.333 1.544 56.12 Lens 32 −21.301 0.167element 3 Second 41 −36.891 0.300 1.607 27.00 lens 42 1.328 0.191element 4 Third 51 −3.560 0.573 1.531 56.00 Lens 52 −0.797 0.080 element5 Fourth 61 1.003 0.385 1.531 56.00 Lens 62 0.680 0.313 element 6Optical 81 ∞ 0.210 1.517 64.00 filter 8 82 ∞ 0.218 Imaging — ∞ −0.006 —— plane 10

In the second preferred embodiment, the object-side surfaces 31, 41, 51,61 and the imaging-side surfaces 32, 42, 52, 62 are aspherical surfacesand may be defined by the aforementioned equation (1). Tables 6 and 7show conic constants (K), and higher-order aspherical surfacecoefficients (A), (B), (C), (D), (E) of the object-side surfaces 31, 41,51, 61 and the imaging-side surfaces 32, 42, 52, 62. It is to be notedthat, in this embodiment, the higher-order aspherical surfacecoefficient (F) of the object-side surfaces 31, 41, 51, 61 and theimaging-side surfaces 32, 42, 52, 62 has a value of “0”, and hence isomitted from Tables 6 and 7.

TABLE 6 Surface K A B 31 1.2003E+00 0.0000E+00 7.7611E−02 32 0.0000E+003.0428E−01 −3.7751E−01 41 0.0000E+00 −1.3938E−01 −1.2157E+00 421.8276E+00 0.0000E+00 −1.0638E+00 51 0.0000E+00 2.5073E−01 −1.4887E+0052 −1.3788E−02 0.0000E+00 1.1743E−01 61 0.0000E+00 −9.3364E−014.8794E−01 62 −9.0662E−01 −1.0326E+00 8.2326E−01

TABLE 7 Surface C D E 31 −9.1967E−02 0.0000E+00 0.0000E+00 32 2.8013E−010.0000E+00 0.0000E+00 41 −1.0664E+00 0.0000E+00 0.0000E+00 42 1.0191E+000.0000E+00 0.0000E+00 51 1.4743E+00 0.0000E+00 0.0000E+00 52 −2.8925E−030.0000E+00 0.0000E+00 61 −1.1042E+00 2.1865E+00 −1.5911E+00 62−8.6586E−01 6.5005E−01 −2.3789E−01

Shown in FIG. 5 from left to right are plots of sagittal astigmatism,tangential astigmatism, and distortion aberrations of the imaging lens 2of the second preferred embodiment at the three representativewavelengths. As shown in the plots of sagittal and tangentialastigmatisms, the imaging lens 2 has a range of focal distances notexceeding ±0.05 mm within the whole angle of view at each of therepresentative wavelengths. Moreover, the distortion aberrations thatoccur in the imaging lens 2 of the second preferred embodiment have arange within ±0.30.

FIG. 6 illustrates ray fan plots of the imaging lens 2 of the secondpreferred embodiment at normalized half-angles of view of 1, 0.8, and 0,which correspond to relative angles of view of 33.00°, 27.58°, and 0°,respectively. It is apparent that the imaging lens 2 is able to achievean angle of view of 66° and low optical aberrations.

Referring to FIG. 7, the third preferred embodiment of this inventionhas a configuration almost identical to that of the first preferredembodiment. The first lens element 3 is a biconvex lens element. Thesecond lens element 4 is a biconcave lens element. The object-sidesurface 51 and the imaging-side surface 52 of the third lens element 5are a concave surface and a convex surface, respectively. Theobject-side surface 61 of the fourth lens element 6 is a wavelikesurface having a convex area 611 in the vicinity of the optical axis (I)of the fourth lens element 6, and the imaging-side surface 62 of thesame is a wavelike surface having a concave area 621 in the vicinity ofthe optical axis (I) of the fourth lens element 6. The aperture stop 7is disposed between the first and second lens elements 3, 4, and isdisposed on the imaging-side surface 32 of the first lens element 3 ofthis invention.

Table 8 shows optical parameters of the lens elements 3-6, the opticalfilter 8, and the imaging plane 10 in the third preferred embodiment.

TABLE 8 Radius of Curvature Thickness Refractive Abbe Surface (mm) (mm)Index Number First 31 1.065 0.332 1.531 56.00 Lens 32 −30.651 0.200element 3 Second 41 −30.653 0.3000 1.607 27.00 lens 42 1.217 0.1535element 4 Third 51 −673.972 0.697 1.531 56.00 Lens 52 −0.697 0.080element 5 Fourth 61 1.450 0.418 1.531 56.00 Lens 62 0.648 0.313 element6 Optical 81 ∞ 0.210 1.517 64.00 filter 8 82 ∞ 0.167 Imaging — ∞ −0.001— — plane 10

In the third preferred embodiment, the object-side surfaces 31, 41, 51,61 and the imaging-side surfaces 32, 42, 52, 62 are aspherical surfacesand may be defined by the aforementioned equation (1). Tables 9 and 10show conic constants (K), and higher-order aspherical surfacecoefficients (A), (B), (C), (D), (E) of the object-side surfaces 31, 41,51, 61 and the imaging-side surfaces 32, 42, 52, 62. It is to be notedthat, in this embodiment, the higher-order aspherical surfacecoefficient (F) of each of the object-side surfaces 31, 41, 51, 61 andthe imaging-side surfaces 32, 42, 52, 62 has a value of “0”, and henceis omitted from Tables 9 and 10.

TABLE 9 Surface K A B 31 1.5909E+00 0.0000E+00 5.5339E−02 32 0.0000E+003.3553E−01 −3.2334E−01 41 0.0000E+00 −2.9897E−01 −7.5085E−01 42−8.3854E−01 0.0000E+00 −6.2382E−01 51 0.0000E+00 7.4113E−02 −6.7356E−0152 −3.9205E−01 0.0000E+00 3.5454E−01 61 0.0000E+00 −1.0339E+008.4838E−01 62 −1.2092E+00 −1.2526E+00 1.4408E+00

TABLE 10 Surface C D E 31 −1.2377E−01 0.0000E+00 0.0000E+00 327.1020E−01 0.0000E+00 0.0000E+00 41 −3.6288E+00 0.0000E+00 0.0000E+00 426.5857E−01 0.0000E+00 0.0000E+00 51 1.1019E+00 0.0000E+00 0.0000E+00 52−3.9701E−01 0.0000E+00 0.0000E+00 61 −5.9630E−01 1.0278E+00 −1.0836E+0062 1.2621E+00 6.2777E−01 −1.6493E−01

Shown in FIG. 8 from left to right are plots of sagittal astigmatism,tangential astigmatism, and distortion aberrations of the imaging lens 2of the third preferred embodiment at the three representativewavelengths. FIG. 9 illustrates ray fan plots of the imaging lens 2 ofthe third preferred embodiment at normalized half-angles of view of 1,0.8, and 0, which correspond to relative angles of view of 33.00°,27.51°, and 0°, respectively. It is apparent that the imaging lens 2 isable to achieve an angle of view of 66° and low optical aberrations.

Referring to FIG. 10, the fourth preferred embodiment of this inventionhas a configuration almost identical to that of the first preferredembodiment. The first lens element 3 is a biconvex lens element. Thesecond lens element 4 is a biconcave lens element. The object-sidesurface 51 and the imaging-side surface 52 of the third lens element 5are a concave surface and a convex surface, respectively. Theobject-side surface 61 of the fourth lens element 6 is a wavelikesurface having a convex area 611 in the vicinity of the optical axis (I)of the fourth lens element 6, and the imaging-side surface 62 of thesame is a wavelike surface having a concave area 621 in the vicinity ofthe optical axis (I) of the fourth lens element 6. The aperture stop 7is disposed between the first and second lens elements 3, 4, and isdisposed on the imaging-side surface 32 of the first lens element 3 inthis embodiment.

Table 11 shows optical parameters of the lens elements 3-6, the opticalfilter 8, and the imaging plane 10 in the fourth preferred embodiment.

TABLE 11 Radius of Curvature Thickness Refractive Abbe Surface (mm) (mm)Index Number First 31 0.942 0.357 1.544 56.12 Lens 32 −5.700 0.107element 3 Second 41 −16.250 0.300 1.607 27.00 lens 42 1.129 0.188element 4 Third 51 −18.518 0.525 1.531 56.00 Lens 52 −1.076 0.080element 5 Fourth 61 0.972 0.310 1.531 56.00 Lens 62 0.723 0.313 element6 Optical 81 ∞ 0.210 1.517 64.00 filter 8 82 ∞ 0.185 Imaging — ∞ −0.022— — plane 10

In the fourth preferred embodiment, the object-side surfaces 31, 41, 51,61 and the imaging-side surfaces 32, 42, 52, 62 are aspherical surfacesand may be defined by the aforementioned equation (1). Tables 12 and 13show conic constants (K), and higher-order aspherical surfacecoefficients (A), (B), (C), (D), (E) of the object-side surfaces 31, 41,51, 61 and the imaging-side surfaces 32, 42, 52, 62. It is to be notedthat, in this embodiment, the higher-order aspherical surfacecoefficient (F) of each of the object-side surfaces 31, 41, 51, 61 andthe imaging-side surfaces 32, 42, 52, 62 has a value of “0”, and henceis omitted from Tables 12 and 13.

TABLE 12 Surface K A B 31 6.6012E−01 0.0000E+00 −4.1214E−02 320.0000E+00 4.6103E−01 −5.0339E−01 41 0.0000E+00 1.9266E−01 −1.5847E+0042 1.7393E+00 0.0000E+00 −1.2067E+00 51 0.0000E+00 5.0072E−01−2.9983E+00 52 3.4241E−02 0.0000E+00 −4.5071E−01 61 0.0000E+00−1.1828E+00 4.6896E−01 62 −1.4151E+00 −1.1188E+00 1.1673E+00

TABLE 13 Surface C D E 31 6.4481E−01 0.0000E+00 0.0000E+00 32−1.6260E−01 0.0000E+00 0.0000E+00 41 −2.2720E−01 0.0000E+00 0.0000E+0042 1.1741E+00 0.0000E+00 0.0000E+00 51 3.6965E+00 0.0000E+00 0.0000E+0052 −3.1569E−02 0.0000E+00 0.0000E+00 61 −1.0668E+00 2.0910E+00−1.4669E+00 62 −1.0752E+00 5.9753.E−01 −1.8835E−01

Shown in FIG. 11 from left to right are plots of sagittal astigmatism,tangential astigmatism, and distortion aberrations of the imaging lens 2of the fourth preferred embodiment at the three representativewavelengths. FIG. 12 illustrates ray fan plots of the imaging lens 2 ofthe fourth preferred embodiment at normalized half-angles of view of 1,0.8, and 0, which correspond to relative angles of view of 33.00°,27.51°, and 0°, respectively. It is apparent that the imaging lens 2 isable to achieve an angle of view of 66° and low optical aberrations.

Table 14 shows optical parameters of the preferred embodiments forcomparison.

TABLE 14 Imaging Height = 1.2 mm Preferred Embodiment 1 2 3 4 F Number2.4 2.4 2.4 2.4 Half-angle of 37.4 33.0 33.0 33.0 view f 1.575 1.8451.851 1.859 TL 2.288 2.764 2.868 2.553 f1 1.598 1.841 1.955 1.522 f2−2.544 −2.127 −1.941 −1.745 f3 1.966 1.183 1.320 2.140 f4 −7.457 −6.806−2.704 −9.374 f12 3.187 4.656 6.584 3.753 R21/f −4.363 −19.999 −16.557−8.741 R12/R21 0.471 0.577 1.000 0.351 Wg 0.086 0.167 0.200 0.107 f1/f1.014 0.998 1.056 0.819 TL/f 1.453 1.498 1.549 1.373 f12/f 2.023 2.5243.556 2.019

It is to be noted that the F number represents a ratio between a focallength of the imaging lens 2 and a diameter of an entrance pupil of theaperture stop 7, and W_(g) represents the width of the gap between thefirst and second lens elements 3, 4.

The imaging lens 2 of each of the preferred embodiments satisfiesoptical conditions 2 to 6, which are described hereinafter.

Optical condition 2:

−21≦R ₂₁ /f<0  (2)

wherein R₂₁ represents a radius of curvature of the object-side surface41 of the second lens element 4, and f represents the focal length ofthe imaging lens 2. The imaging lens 2 must satisfy optical condition 2such that chromatic aberrations may be significantly reduced andstronger bonding between the imaging-side surface 32 of the first lenselement 3 and the object-side surface 41 of the second lens element 4may be ensured.

Optical condition 3:

R ₁₂ /R ₂₁≦1.1  (3)

wherein R₁₂ represents a radius of curvature of the imaging-side surface32 of the first lens element 1. The imaging lens 2 must satisfy opticalcondition 3, and the gap between the first and second lens elements 3, 4must have a width not narrower than 0.08 mm, so as to alleviateperipheral interference between the first and second lens elements 3, 4,which may influence the structural integrity of the imaging lens 2.

Optical condition 4:

0.7<f ₁ /f≦1.1  (4)

wherein f₁ represents a focal length of the first lens element 3.

If the value of f₁/f is greater than 1.1, the positive focusing power ofthe first lens element 3 will be too low and must be compensated for bythe other lens elements 4-6, which, as a consequence, will increase theoverall length of the imaging lens 2. On the other hand, if the value off₁/f is not greater than 0.7, the positive focusing power of the firstlens element 3 will be too high, causing the first lens element 3 toexhibit severe distortion aberration. Although the other lens element4-6 may be configured to compensate for the low positive focusing powerof the first lens element 3, the effect of which is rather limited sincedesign of the imaging lens 2 is substantially based upon the first lenselement 3.

Optical condition 5:

TL/f<1.55  (5)

wherein TL represents a distance between the object-side surface 31 ofthe first lens element 3 and the imaging plane 10. If the imaging lens 2fails to satisfy optical condition 5, the overall length thereof will betoo long, rendering it less applicable to miniaturized products.

Optical condition 6:

1<f ₁₂ /f<4.5  (6)

wherein f₁₂ represents a combined focal length of the first and secondlens elements 3, 4.

If the value of f₁₂/f is not smaller than 4.5, the combined focal lengthof the first and second lens elements 3, 4 will be too long. That is tosay, a combined positive focusing power of the first and second lenselements 3, 4 will be too low. Further, compensation by the other lenselements 5-6 will be insufficient to shorten the combined focal lengthsignificantly. If the value of f₁₂/f is not larger than 1, the combinedfocal length of the first and second lens elements 3, 4 will be tooshort. That is to say, the combined positive focusing power of the firstand second lens elements 3, 4 will be too high. As a result, the firstand second lens elements 3, 4 in combination will exhibit highdistortion aberration. Moreover, the effect of compensation by the otherlens elements 5-6 will be rather limited.

Referring to FIG. 13, the preferred embodiment of an electronicapparatus 1 according to this invention includes a housing 11 and animaging module 12 disposed in the housing 11. In this embodiment, theelectronic apparatus 1 is exemplified as a mobile phone. However, inother embodiments, the electronic apparatus 1 may be implementedotherwise. The imaging module 12 includes the imaging lens 2 of thefirst preferred embodiment, and an image sensor 121 disposed at theimaging plane 10.

In summary, the imaging lenses 2 of the preferred embodiments haverelatively low sagittal and tangential astigmatisms, distortionaberrations, and chromatic aberrations, and have a relatively wide angleof view.

Furthermore, the first, second, third, and fourth lens elements 3-6 aremade of plastic and hence have low weights and may be fabricated atlower costs.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation so as toencompass all such modifications and equivalent arrangements.

What is claimed is:
 1. An optical imaging lens comprising, from anobject side to an image side: a first lens element; a second lenselement; a third lens element; and a fourth lens element, wherein eachof the first lens element, the second lens element, the third lenselement, and the fourth lens element have an object-side surface facingtoward the object side and an image-side surface facing toward the imageside, wherein: the first lens element has a positive refracting power,the object-side surface of the first lens element has a convex portionin a vicinity of an optical axis and a convex portion near acircumference of the first lens element, and the image-side surface ofthe first lens element has a convex portion in a vicinity of the opticalaxis and a convex portion near the circumference of the first lenselement; the second lens element has a negative refracting power, theobject-side surface of the second lens element has a concave portion ina vicinity of the optical axis and a concave portion near acircumference of the second lens element, and the image-side surface ofthe second lens element has a concave portion in a vicinity of theoptical axis; the third lens element has a positive refracting power,the object-side surface of the third lens element has a concave portionin a vicinity of the optical axis, and the image-side surface of thethird lens element has a convex portion in a vicinity of the opticalaxis; the fourth lens element has a negative refracting power and theimage-side surface of the fourth lens element has a concave portion in avicinity of the optical axis and a convex portion near a circumferenceof the fourth lens element; the optical imaging lens has only four lenselements having a refracting power; and the optical imaging lenssatisfies the following relations: 0.430≦AG12/AG23≦1.303, wherein AG12is a width of an air gap between the first and second lens elementsalong the optical axis and AG23 is a width of an air gap between thesecond and third lens elements along the optical axis.
 2. The opticalimaging lens of claim 1 wherein a ratio T1/T3 is between 0.476 and0.952, wherein T1 is a thickness of the first lens element along theoptical axis and T3 is a thickness of the third lens element along theoptical axis.
 3. The optical imaging lens of claim 1 wherein a ratioT1/AG12 is between 1.660 and 3.488, wherein T1 is a thickness of thefirst lens element along the optical axis.
 4. The optical imaging lensof claim 1, wherein a ratio T3/AG34 is between 3.938 and 8.713, whereinT3 is a thickness of the third lens element along the optical axis andAG34 is a width of an air gap between the third and fourth lens elementsalong the optical axis.
 5. An optical imaging lens comprising, from anobject side to an image side: a first lens element; a second lenselement; a third lens element; and a fourth lens element, wherein eachof the first lens element, the second lens element, the third lenselement, and the fourth lens element have an object-side surface facingtoward the object side and an image-side surface facing toward the imageside, wherein: the first lens element has a positive refracting power,the object-side surface of the first lens element has a convex portionin a vicinity of an optical axis and a convex portion near acircumference of the first lens element, and the image-side surface ofthe first lens element has a convex portion in a vicinity of the opticalaxis and a convex portion near the circumference of the first lenselement; the second lens element has a negative refracting power, theobject-side surface of the second lens element has a concave portion ina vicinity of the optical axis and a concave portion near acircumference of the second lens element, and the image-side surface ofthe second lens element has a concave portion in a vicinity of theoptical axis; the third lens element has a positive refracting power andthe object-side surface of the third lens element has a concave portionin a vicinity of the optical axis; the fourth lens element has anegative refracting power, the image-side surface of the fourth lenselement has a concave portion in a vicinity of the optical axis, and aconvex portion near a circumference of the fourth lens element; theoptical imaging lens has only four lens elements having a refractingpower; and the optical imaging lens satisfies the following relations:1.000≦T2/AG23≦1.954; and 13.938≦ALT/AG34≦21.838, wherein T2 is athickness of the second lens element along the optical axis, AG23 is awidth of an air gap between the second and third lens elements along theoptical axis, ALT is a sum of thicknesses of the first lens element tothe fourth lens element, and AG34 is a width of an air gap between thethird and fourth lens elements along the optical axis.
 6. The opticalimaging lens of claim 5 wherein a ratio AG12/AAG is between 0.235 and0.461, wherein AG12 is a width of an air gap between the first andsecond lens elements along the optical axis, and AAG is a sum of widthsof air gaps between the first to fourth lens elements.
 7. The opticalimaging lens of claim 5 wherein a ratio T3/AG23 is between 1.575 and4.541, wherein T3 is a thickness of the third lens element along theoptical axis.
 8. The optical imaging lens of claim 5 wherein a ratioT3/AAG is between 0.861 and 1.608, wherein T3 is a thickness of thethird lens element along the optical axis, and AAG is a sum of widths ofair gaps between the first lens element to the fourth lens element. 9.An optical imaging lens comprising, from an object side to an imageside: a first lens element; a second lens element; a third lens element;and a fourth lens element, wherein each of the first lens element, thesecond lens element, the third lens element, and the fourth lens elementhave an object-side surface facing toward the object side and animage-side surface facing toward the image side, wherein: the first lenselement has a positive refracting power, the object-side surface of thefirst lens element has a convex portion in a vicinity of an optical axisand a convex portion near a circumference of the first lens element, andthe image-side surface of the first lens element has a convex portion ina vicinity of the optical axis and a convex portion near thecircumference of the first lens element; the second lens element has anegative refracting power, the object-side surface of the second lenselement has a concave portion in a vicinity of the optical axis and aconcave portion near a circumference of the second lens element, and theimage-side surface of the second lens element has a concave portion in avicinity of the optical axis and a concave portion near thecircumference of the second lens element; the third lens element has apositive refracting power, the object-side surface of the third lenselement has a concave portion in a vicinity of the optical axis and aconcave portion near a circumference of the third lens element, and theimage-side surface of the third lens element has a convex portion in avicinity of the optical axis and a convex portion near the circumferenceof the third lens element; the fourth lens element has a negativerefracting power and the image-side surface of the fourth lens elementhas a concave portion in a vicinity of the optical axis and a convexportion near a circumference of the fourth lens element; the opticalimaging lens has only four lens elements having a refracting power; andthe optical imaging lens satisfies the following relations:0.430≦T2/T3≦0.653; 1.050≦T3/T4≦1.694; and 0.930≦T1/(AG12+AG23)≦1.210,wherein T1 is a thickness of the first lens element along the opticalaxis, T2 is a thickness of the second lens element along the opticalaxis, T3 is a thickness of the third lens element along the opticalaxis, T4 is a thickness of the fourth lens element along the opticalaxis, AG12 is a width of an air gap between the first and second lenselements along the optical axis, and AG23 is a width of an air gapbetween the second and third lens elements along the optical axis. 10.The optical imaging lens of claim 9 wherein a ratio T2/T4 is between0.667 and 0.968.
 11. The optical imaging lens of claim 9 wherein a ratioT3/ALT is between 0.283 and 0.399, wherein ALT is a sum of thicknessesof the first to fourth lens elements.
 12. The optical imaging lens ofclaim 11 wherein a ratio AG12/AG34 is between 1.075 and 2.500, whereinAG34 is a width of an air gap between the third and fourth lens elementsalong the optical axis.
 13. An optical imaging lens comprising, from anobject side to an image side: a first lens element; a second lenselement; a third lens element; and a fourth lens element, wherein eachof the first lens element, the second lens element, the third lenselement, and the fourth lens element have an object-side surface facingtoward the object side and an image-side surface facing toward the imageside, wherein: the first lens element has a positive refracting power,the object-side surface of the first lens element has a convex portionin a vicinity of an optical axis and a convex portion near acircumference of the first lens element, and the image-side surface ofthe first lens element has a convex portion in a vicinity of the opticalaxis and a convex portion near the circumference of the first lenselement; the second lens element has a negative refracting power, theobject-side surface of the second lens element has a concave portion ina vicinity of the optical axis and a concave portion near acircumference of the second lens element, and the image-side surface ofthe second lens element has a concave portion in a vicinity of theoptical axis and a concave portion near the circumference of the secondlens element; the third lens element has a positive refracting power,the object-side surface of the third lens element has a concave portionin a vicinity of the optical axis and a concave portion near acircumference of the third lens element, and the image-side surface ofthe third lens element has a convex portion in a vicinity of the opticalaxis and a convex portion near the circumference of the third lenselement; the fourth lens element has a negative refracting power, theobject-side surface of the fourth lens element has a convex portion in avicinity of the optical axis, and the image-side surface of the fourthlens element has a concave portion in a vicinity of the optical axis anda convex portion near a circumference of the fourth lens element; theoptical imaging lens has only four lens elements having a refractingpower; and the optical imaging lens satisfies the following relations:0.430≦T2/T3≦0.653; 0.208≦T4/ALT≦0.269; and 1.366≦(T1+T2)/AAG≦1.752,wherein T1 is a thickness of the first lens element along the opticalaxis, T2 is a thickness of the second lens element along the opticalaxis, T3 is a thickness of the third lens element along the opticalaxis, T4 is a thickness of the fourth lens element along the opticalaxis, ALT is a sum of thicknesses of the first to fourth lens elements,and AAG is a sum of widths of air gaps between the first to fourth lenselements.
 14. The optical imaging lens of claim 13 wherein a ratio T3/T4is between 1.050 and 1.694.
 15. The optical imaging lens of claim 13wherein a ratio T1/(AG12+AG23) is between 0.930 and 1.210, wherein AG12is a width of an air gap between the first and second lens elementsalong the optical axis, and AG23 is a width of an air gap between thesecond and third lens elements along the optical axis.
 16. The opticalimaging lens of claim 15, wherein a ratio T1/AG34 is between 3.750 and4.463, wherein AG34 is a width of an air gap between the third andfourth lens elements along the optical axis.
 17. The optical imaginglens of claim 13 wherein a ratio T2/T4 is between 0.667 and 0.968. 18.The optical imaging lens of claim 13 wherein a ratio T3/ALT is between0.283 and 0.399.